half arsed comes from the term half arzed, in relation to the bevelled edges on a mantle peice. In the old day's they would arze the front and the back, but poorer(or smarter) people started to just get the front done because the back is against the wall. Hence the term half arzed or arsed meaning half done effort. Sorry if thats no help but I was just goin with the flow. Steel's where it's at anyway